用Jq遍历一个div里面的所有input 并判断是否为空？

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <script src="scripts/jquery-1.7.2.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(function () {
            $("#btnSubmit").click(function () {
                $("input[type='text']").each(function () {
                    if ($(this).val() == "") {
                        alert("不能为空！");
                    }
                })
            })
        })
    </script>
</head>
<body>
    <div id="test">
        <input type="text" id="txtName" />
        <input type="text" id="txtPwd" />
        <input type="button" id="btnSubmit" value="提 交" />
    </div>
</body>
</html>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <script src="scripts/jquery-1.7.2.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(function () {
            $("#btnSubmit").click(function () {
                $("div").find("input[type='text']").each(function () {
                    if ($(this).val() == "") {
                        alert("不能为空！");
                    }
                })
            })
        })
    </script>
</head>
<body>
    <div id="test">
        <input type="text" id="txtName" />
        <input type="text" id="txtPwd" />
        <input type="button" id="btnSubmit" value="提 交" />
    </div>
</body>
</html>